Electric glow discharge tube



' P M. J. DRUYVESTEYN 1,972,647

ELECTRIC GLOW DISCHARGE TUBE Filed May 28, 1931 Patented Sept. 4, 19341,972,647 ELECTRIC GLOW DISCHARGE TUBE Mari Johan Druyvesteyn,Eindhoven, Netherlands, assignor to N. V. Philips Gloeilampenfabneken,Eindhoven, Netherlands Application May 28, 1931, Serial No. 540,707 Inthe Netherlands July 26, 1930 4 Claims. (01. 176-122) This inventionrelates'to an electric glow discharge tube containing cold electrodesand a gaseous filling. In referring to a gaseous filling it is intendedhereinafter to include not 5 only a filling consisting of one or moregases but also a filling consisting of one or more vapours or a mixtureof gas and vapour.

As is well known, the voltage to be impressed on the electrodes of sucha glow discharge tube in order to start the discharge is higher than thepotential difference existing between the electrodes once the dischargeis struck. This difference between the starting potential and theoperating voltage is frequently very objectionable.

The invention has for its object to lower the starting voltage of a glowdischarge tube and thus to decrease the difference between the startingvoltage and the operating voltage.

According to the invention, for this purpose a grid-shaped auxiliaryelectrode is arranged between the electrodes, which auxiliary electrodeis electrically connected to the anode. The grid-shaped auxiliaryelectrode, has the same potential as the anode so that there is betweenthem a space substantially free from any electric field; this is foundto bring about a reduction of the starting voltage, also termed thebreak-down voltage.

Preferably, the distance between the main electrodes, and thecomposition and the pressure of the gaseous filling are so selected thatthe voltage necessary for starting the discharge between the mainelectrodes be a minimum in the absence of the grid shaped electrode.Even in this case, the provision of the grid-shaped auxiliary electrodeis found to favourably influence the starting voltage.

The starting voltage of the discharge tube may be given a very low valueby causing the 40 active surface of the cathode to be constituted by analkali metal layer applied to an alkali oxide.

In order that the invention may be clearly understood and readilycarried into effect a luminous discharge tube, according to theinvention will be described more fully by way of example with referenceto the accompanying drawing, the single figure of which is adiagrammatic view of a discharge tube embodying the invention.

Referring to the figure, the tube has a bulb 1 into which is sealed apinch 2. This pinch has secured thereto three electrodes; namely, ananode 3, a cathode 4 and an auxiliary electrode 5.

The anode is formed by a metal disc, consisting for example of nickel,carried by a pole wire 6.

This pole wire also supports the auxiliary electrode 5. This auxiliaryelectrode is constituted by a grid-shaped member, for example, a pieceof wire gauze. The cathode 4 is constituted similarly to the anode 3 bya small metal .disc secured to a pole wire 7 and coated over its surfacewith a layer of caesium oxide to which a layer of caesium is applied.This cathode surface may be formed subsequent to the exhaustion of thetube by liberating and depositing a small quantity of caesium from, acapsule 8, for example, arranged within the tube and containing acaesium compound, such for example, as caesium chromate, and a reducingagent, for example zirconium. When this capsule is subjected to highfrequency heating the caesium compound is reduced and the caesium isliberated. Thus, the caesium is precipitated on the wall and thecomponent members of the discharge tube. By gently heating the outerwall of the discharge tube, the caesium is expelled from the inner walland is precipitated on the electrodes. If it is desired to prevent thecaesium from being precipitated on the anode, the latter may be formedof a material to which the caesium does not adhere firmly whereas thesurface of the cathode is formed for example of nickel, preferablyoxidized, to which the caesium adheres well.

After the caesium film is formed on the cathode, a small quantity ofoxygen is admitted into the tube.to convert the caesium-film intocaesium oxide.

After the excess oxygen has been removed, a small quantity of caesium isagain introduced in the tube, for example from a second capsule 9. tothe cathode surface where This caesium is applied it is precipitated onthe caesium oxide film previously formed to which it adheres veryreadily.

It is found that such a cathode considerably lowers the starting voltageof the glow discharge.

Subsequent to the formation of the cathode surface, a suitable gaseousfilling, consisting, for example, of a rare gas, is introduced in thedischarge tube.

Satisfactory results have been oba minimum (Paschens law).

In the use of the gaseous filling described, the most favourabledistance between the main electrodes was found to be about 15 mm.

If a grid shaped auxiliary electrode is arranged between the electrodes3 and 4, the starting voltage of the luminous discharge tube is furtherlowered. The starting voltage was, in the absence of the auxiliaryelectrode, 66 volts; the provision of the auxiliary electrode was foundto reduce this voltage to 47 volts, the

operating voltage being in either case 36 volts.

and the pressure of said gaseous filling being so selected that thestarting voltage of the discharge between said cathode and said anode isa minimum according to the law of Paschen, and a grid-shaped auxiliaryelectrode arranged between said cathode and anode and electricallyconnected to said anode said auxiliary electrode reducing the startingvoltage of the discharge tube below said minimum.

2. An electric glow discharge tube comprising a cold cathode, an anodeand a gaseous filling consisting of neon to which percent argon isadded, the pressure of said gaseous filling being approximately 6 mm,the distance between said cathode and said anode being approximately 15mm, a grid-shaped auxiliary electrode mounted between said cathode andsaid anode and electrically connected to said anode.

3. An electric glow discharge tube, comprising cold main electrodes,including a cathode and an anode, a gaseous filling, and a grid shapedauxiliary electrode disposed between said cathode and anode and inproximity of said anode, and being in direct electric connection withsaid anode.

4. An electric glow discharge tube comprising, a cold' cathode and ananode, a gaseous filling, said cathode having an active surfaceconsisting of an alkali oxide layer to which an alkali metal layer isapplied, the distance between said cathode and said anode and thepressure of said gaseous filling being so selected that the startingvoltage of the discharge between said cathode and said anode is aminimum according to the law of Paschen, and a grid-shaped auxiliaryelectrode disposed between said cathode and anode and electricallyconnected to said anode, said auxiliary electrode reducing the startingvoltage below said minimum.

MARI J OHAN DRUYVESTEYN.

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